STRESS INTENSITY FACTORS AND WEIGHT-FUNCTIONS FOR LONGITUDINAL SEMIELLIPTIC SURFACE CRACKS IN THIN PIPES

Three-dimensional finite element analyses have been conducted to calcu late the stress intensity factors for internal and external low aspect ratio longitudinal semi-elliptic cracks in pipes with a ratio of inte rnal radius to thickness of 10. The stress intensity factors are prese nted for the deepest and surface points for semi-elliptic cracks with aspect ratios of 0.05 and 0.1, and a/t values of 0.2, 0.5, and 0.8. Un iform, linear, parabolic or cubic stress distributions were applied to the crack face. The results for uniform and linear stress distributio ns were combined with corresponding results for higher aspect ratio su rface cracks and edge cracks to derive the weight function over the en tire range 0 less than or equal to a/c less than or equal to 1 and 0 l ess than or equal to a/t less than or equal to 0.8. The weight functio n is then verified against finite element data for the parabolic or cu bic stress distributions. Results were within 5% for both the surface point and the deepest point.